274 THE ILLINOIS GLACIAL LOBE. 



same distance (from 573 to 490 feet), and the terrace maintains a somewhat 

 regular altitude above it, being- about 65 or 70 feet above it at the outer 

 border of the moraine and 50 feet at the border of the Illinois Valley. The 

 terrace apparently has little fall in the 3 or 4 miles occupied in crossing the 

 moraine. The remnants of the terrace occupy nearly one-third of the 

 width of the valley. Several good exposures of the gravel were found, and 

 these cmite uniformly show a coarse gravel and cobble near the surface of 

 the terrace, with finer gravel below. The coarseness of the material is such 

 as to indicate vigorous drainage, apparently stronger than that of the 

 present stream. 



A small northern tributary of the Mackinaw, Deer Creek, emerges 

 from the moraine a few miles north from the point where the Mackinaw 

 leaves it. This also carries deposits of gravel along the borders of the 

 valley. It is preserved in small remnants flanking the slopes up a height 

 of 20 or 25 feet above the creek at the point where the stream leaves the 

 moraine. The upland plain stands about 20 feet higher than the upper 

 limits of the gravel. 



On Farm Creek, a tributary of the Illinois, entering opposite Peoria, 

 there is a gravel deposit heading in the midst of the Bloomington system 

 about 2 miles west of Washington. This has been traced continuously 

 down to the Illinois River Valley, a distance of 8 miles. At its head it is 

 nearly as low as the creek flood plain, being scarcely 10 feet above the 

 stream, but its fall is far less rapid than that of the creek. The creek has 

 a fall of about 180 feet in the 8 miles while the terrace falls scarcely 60 

 feet. At Farmdale the terrace stands about 85 feet above the creek and at 

 East Peoria about 120 feet. The depth of the gravel on this teiTace is 

 usually only 15 or 20 feet, including a silt capping 3 or 4 feet in depth. 

 The breadth of the valley in which it is deposited was apparently one- 

 eighth to one-fourth of a mile. The present stream has in places formed a 

 valley of greater width, but usually it is confined to narrower limits than 

 the old valley. The valley in which the gravel filling was made had been 

 nowhere cut to a depth of more than 40 or 50 feet below the bordering 

 plain outside the Bloomington moraine, and the gravel filling has reduced 

 this depth to about 25 feet. The work performed by the stream which 

 preceded the gravel filling was therefore but a small fraction of the amount 

 performed by Farm Creek since that filling. 



